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authorPeter De Schrijver <pdeschrijver@nvidia.com>2014-06-12 18:58:28 +0300
committerStephen Warren <swarren@nvidia.com>2014-06-16 12:48:07 -0600
commit5930c1a1f7f8439883d0a2173c6ce51d577e36ec (patch)
treed1cbc3e409c5c534d2c9113fdb0f0ebff16ba410 /arch/arm/lib
parente6639117d624d5c8f531d22456a69e38dc23c501 (diff)
downloadlinux-linaro-stable-5930c1a1f7f8439883d0a2173c6ce51d577e36ec.tar.gz
ARM: choose highest resolution delay timer
In case there are several possible delay timers, choose the one with the highest resolution. This code relies on the fact secondary CPUs have not yet been brought online when register_current_timer_delay() is called. This is ensured by implementing calibration_delay_done(), Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com> Acked-by: Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by: Stephen Warren <swarren@nvidia.com>
Diffstat (limited to 'arch/arm/lib')
-rw-r--r--arch/arm/lib/delay.c26
1 files changed, 22 insertions, 4 deletions
diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c
index 5306de350133..312d43eb686a 100644
--- a/arch/arm/lib/delay.c
+++ b/arch/arm/lib/delay.c
@@ -19,6 +19,7 @@
* Author: Will Deacon <will.deacon@arm.com>
*/
+#include <linux/clocksource.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/kernel.h>
@@ -36,6 +37,7 @@ struct arm_delay_ops arm_delay_ops = {
static const struct delay_timer *delay_timer;
static bool delay_calibrated;
+static u64 delay_res;
int read_current_timer(unsigned long *timer_val)
{
@@ -47,6 +49,11 @@ int read_current_timer(unsigned long *timer_val)
}
EXPORT_SYMBOL_GPL(read_current_timer);
+static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
+{
+ return (cyc * mult) >> shift;
+}
+
static void __timer_delay(unsigned long cycles)
{
cycles_t start = get_cycles();
@@ -69,18 +76,24 @@ static void __timer_udelay(unsigned long usecs)
void __init register_current_timer_delay(const struct delay_timer *timer)
{
- if (!delay_calibrated) {
- pr_info("Switching to timer-based delay loop\n");
+ u32 new_mult, new_shift;
+ u64 res;
+
+ clocks_calc_mult_shift(&new_mult, &new_shift, timer->freq,
+ NSEC_PER_SEC, 3600);
+ res = cyc_to_ns(1ULL, new_mult, new_shift);
+
+ if (!delay_calibrated && (!delay_res || (res < delay_res))) {
+ pr_info("Switching to timer-based delay loop, resolution %lluns\n", res);
delay_timer = timer;
lpj_fine = timer->freq / HZ;
+ delay_res = res;
/* cpufreq may scale loops_per_jiffy, so keep a private copy */
arm_delay_ops.ticks_per_jiffy = lpj_fine;
arm_delay_ops.delay = __timer_delay;
arm_delay_ops.const_udelay = __timer_const_udelay;
arm_delay_ops.udelay = __timer_udelay;
-
- delay_calibrated = true;
} else {
pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
}
@@ -91,3 +104,8 @@ unsigned long calibrate_delay_is_known(void)
delay_calibrated = true;
return lpj_fine;
}
+
+void calibration_delay_done(void)
+{
+ delay_calibrated = true;
+}